As a producing process of propylene oxide, there is known a process in which an organic peroxide with propylene is reacted in the presence of an epoxidation catalyst.
In a liquid reaction mixture obtained by the reaction, water, hydrocarbons and oxygen-containing compounds such as methanol, formaldehyde, propionaldehyde, acetone and methyl formate, as impurities, are contained in addition to propylene oxide as a target product. Therefore, multi-stage purification steps become necessary to separate and recover propylene oxide of high purity from the liquid reaction mixture.
In purification of propylene oxide, it is publicly known to subject to extractive distillation using a hydrocarbon as an extractant. For example, U.S. Pat. No. 3,843,488 discloses that an alkane such as octane is effective for removing hydrocarbon impurities having 6 carbon atoms. Further, JP 50-007571 B discloses that an alkane such as octane is effective for removal of water. Furthermore, U.S. Pat. No. 5,133,839 discloses that a hydrocarbon such as octane is effective for removal of impurities such as methanol, propionaldehyde and acetone.
However, according to studies of the present inventors, in the above-described method, effective separation of aldehydes contained in propylene oxide was difficult.